1. Field of the Invention
The present invention relates to solutions of polyimide-forming substances, containing
A) polyamines and PA1 B) amides or esters or a mixture of amides and esters of tetracarboxylic acids, the amide or ester groups carrying substituents selected from the group consisting of carboxyl, sulfo, silyl and siloxyl groups. PA1 A) polyamines and PA1 B) amides or esters or a mixture of amides and esters of tetracarboxylic acids, the amide or ester groups carrying substituents selected from the group consisting of carboxyl, sulfo, silyl and siloxyl groups.
The present invention furthermore relates to the use of such solutions as coating materials and to articles coated with a polyimide.
An important field of use of the polyimide coatings, which are solutions of polyimide-forming substances, is microelectronics, where polyimide coatings are used as insulation layers in the structures of microchips or as buffer layers between the finished chip and the chip housing.
2. Description of the Related Art
An important requirement for the polyimide layers is good adhesion to the base material of the chips, ie. to wafers of silicon or modified silicon. This problem has been solved to date by pretreating the inorganic substrates with adhesion promoters, for example aminoalkoxysilanes, or by adding adhesion-promoting substances to the coating solutions.
Thus, DE-A 41 07 664 describes solutions of polycondensates having nitrogen-heterocyclic structural units, to which azidosilanes are added as adhesion promoters.
A further requirement for such polyimide coatings is very low water absorption, in order to ensure functioning of the microchips even under humid conditions. Since the imide group is known to be hydrophilic, attempts have been made to compensate this by the use of very hydrophobic polyimides, for example by using starting materials having a very high molecular weight in order to reduce the imide group density in the polymer.
It is also desirable to obtain structurable polyimide coatings. For this purpose, the polyimide layers are first predried and then coated with a photoresist. Imagewise exposure is then effected through a mask and, as a rule, development is then carried out with dilute aqueous alkali solutions. As a result, the photoresist can be removed in the exposed parts. In the next step, the polyimide coat, too, is then removed from the developed parts, and the predried polyimide layer is structured in this manner. For structuring under photoresists with aqueous alkaline developers, the polyimide intermediates must be predried to such an extent that they are no longer attacked by the photoresist or the solvents present therein.
However, particularly when polyimide intermediates which can be cured to give polyimides having low water absorption are used, problems are encountered in the development because, after sufficient predrying, said polyimides can no longer be dissolved by aqueous alkaline developers.